In recent years, electrophotographic equipment which employs an electrophotographic process, such as copiers, printers, and facsimile machines, has been widely used. In the electrophotographic equipment, generally, a latent image is formed on a latent image-bearing member, such as a photosensitive drum, a toner is made to adhere onto the latent image, and the latent image is visualized by development as a toner image. By transferring the toner image onto a recording medium, such as paper, an image is formed.
In such electrophotographic equipment, as a developing member which develops a latent image, development rolls have been widely used. For example, a development roll has a structure in which a rubber elastic layer including one or two layers is disposed on the outer circumferential surface of a shaft body, and a surface layer is disposed on the outer circumferential surface of the rubber elastic layer.
For example, Japanese Patent No. 4200625 discloses that, in a development roll having an elastic layer on the outer circumference of a shaft body, a liquid silicone rubber composition in which carbon black is dispersed is used as a material for the elastic layer.
Furthermore, Japanese Patent No. 4193193 discloses a development roll in which a conductive rubber member made of a rubber-like elastic body containing a specific ionic liquid as a conductive agent is disposed on the outer circumference of a shaft body.
However, in the existing development rolls, there is room for improvement in terms of the following points. That is, in the development roll of Japanese Patent No. 4200625, since a liquid silicone rubber is used as a main material for the elastic layer, the development roll exhibits low hardness and good resistance to becoming permanently set. However, since electronically conductive carbon black is dispersed as a conductive agent, uniformity in resistance is influenced by the degree of dispersion of carbon black. Furthermore, since the liquid silicone rubber, which is a matrix polymer, has an insulating property, the conducting path on the molecular level cannot be secured, resulting in poor electrical responsiveness.
On the other hand, in the development roll of Japanese Patent No. 4193193, since an ionic liquid is used, excellent uniformity in resistance is exhibited. However, since the conduction type is ionic conduction, it is not possible to sufficiently decrease the resistance. Furthermore, there may be a possibility of bleeding and blooming depending on the amount of ionic liquid added.
Furthermore, this kind of development roll is required to have a good charge decaying property. The reason for this is that if there is a difference in charge decaying property in the circumferential direction or in the longitudinal direction of the roll, a difference occurs in toner retention, resulting in unevenness in image density. Moreover, if the charge decaying property is low, the toner cleaning capability of a toner feed roll or the like degrades. As a result, toner filming becomes likely to occur, and the charging property decreases, causing a problem of increased fog density. However, in the existing development rolls, the charge decaying property is not sufficient.